Studies of 3T3 cells transformed by a thermosensitive mutant, ts-a, of polyoma virus will be continued. The organization of the viral sequences integrated in the cell DNA of two sublines,1 and 15, and their noninducible derivative will be compared with the structure of the oligomeric DNA at 32 degrees C by the two sublines. BIBLIOGRAPHIC REFERENCES: (a) Francke, B., and M. Vogt. In Vitro Polyoma DNA Synthesis: Self-Annealing Properties of Short DNA Chains. Cell, 5, 205-2ll (l975). (b) Vogt, M., L. T. Bacheler, and L. Boice. Proposed structure of Two Defective Viral DNA Oligomers Produced in 3T3 Cells Transformed by the ts-a Mutant of Polyoma. J. Virol., in press.